Zoom lens

ABSTRACT

A foldable zoom lens system including a simple triplet fixed portion and a zoom portion that includes a reversed-telephoto front objective with a mirror between the negative and positive components of this objective; a movable zooming component; and a compensating component. Another mirror is located between the zoom portion and the fixed portion to provide a compact zoom system that is folded twice. The front objective includes a fixed first component and a second component which is movable for focusing the lens for various subject distances.

UllllCu mean: U Straw et al.

[54] ZOOM LENS [72] inventors: Kimball Straw; William H. Price, both ofRochester, NY.

[73] Assignce: Eastman Kodak Company, Rochester,

[22] Filed: Sept. 8, 1970 [2i] Appl.No.: 70,170

[52] U.S. Cl .l350/l84, 350/186, 350/202 [51] Int. Cl. ..G02b 15/16 [58]Field of Search ..350/1 84, 186, 202

[56] References Cited UNITED STATES PATENTS 1,145,132 7/1915 Florian..350/202 1 Mar. 14, 1972 FOREIGN PATENTS OR APPLICATIONS PrimaryExaminer-John K. Corbin AttorneyRobert W. Hampton and D. Peter Hochberg1 ABSTRACT A foldable zoom lens system including a simple triplet fixedportion and a zoom portion that includes a reversed-telephoto frontobjective with a mirror between the negative and positive components ofthis objective; a movable zooming component; and a compensatingcomponent. Another mirror is located between the zoom portion and thefixed portion to provide a compact zoom system that is folded twice. Thefront objective includes a fixed first component and a second componentwhich is movable for focusing the lens for various subject distances.

1 Claim, 2 Drawing Figures Great Britain ..350/ l 86 v Patented March14, 1972 3,649,101

KIMBALL RAW WILLIAM cs mvsm'o r BY 2 t l A T TORNE YS ZOOM LENS CROSS-REFERENCE TO RELATED APPLICATIONS Reference is made to commonlyassigned and copending US. Pat. applications: Ser. No. 57,663, entitledCamera Format," filed July 23, 1970 in the names of Dianne B. Ainsly andArthur H. Crapsey; Serial No. 57,66l, entitled "Adjusting Mechanism forZoom Lens System, filed July 23, 1970 in the name of Arthur H. Crapsey;and Serial No. 70, I69, entitled Zoom Lens, filed Sept. 8, I970 in thename of William H. Price.

BACKGROUND OF THE INVENTION 1. Field of the Invention I This inventionrelates to zoom lenses, and in particular to compact foldable zoomlenses particularly adapted for use in cinematographic cameras of thetype having a reflex viewfinder.

2. Description of the Prior Art Most prior art zoom lenses, particularlythose in cinematographic cameras, occupy an objectionably large amountof space to provide adequate room for relative movement of the lenscomponents. This difficulty is compounded by the fact that the largestdimension of such lenses usually must be added to one of the long cameradimensions, which tends to make the camera unwieldy. Motion picturecameras generally are arranged in this manner to align the optical axisof the lens perpendicular to the camera's exposure aperture or film gatewhich generally is parallel with the cameras shortest dimen- SIOn.

A camera has been developed recently which has a rectangularparallelepiped shape with its shortest dimension being its depthdimension which extends forwardly from the photographer, as disclosed inthe previously cited US. Pat. application Ser. No. 57,663.

To accomplish such a reorientation of camera dimensions, the film gateis arranged in a plane perpendicular to the object plane of the camera'slens system, which requires a folded optical system. The folding of theoptical system has the further advantage of reducing the largestdimension of the lens to render it commensurate with the reduced depthdimension of the camera.

In addition, the focusing of prior zoom lenses for different subjectdistances has generally been accomplished by moving the front objective.Since this requires that the front component of the system be movable,the lens mounts must be large and cumbersome, and cannot be fully sealedagainst dust and moisture. These materials are objectionable in anyoptical system, and are particularly harmful in a zoom lens since zoomlenses contain many moving parts. A zoom lens is known comprising afixed front component and movable rear zoom components, wherein focusingfor different subject distances is accomplished by moving the zoomcomponents, but this is done at the expense of changing the zoom rangewhen the lens is focused.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a folded zoom optical system having a short length.

Another object is to provide an improved zoom lens having a wide fieldangle.

A further object is to provide a compact folded zoom system for acinematographic camera having a small depth dimension and including areflex viewfinder.

A still further object is to provide a zoom lens system having adequatespace between its components for reflectors that change the direction ofits optical axis.

Yet another object is to provide a zoom lens adapted to focus ondifferent subject distances without altering the zoom range, wherein thefront lens component is fixed so that the lens can be sealed to protectthe lens and camera interior against the entry of harmful materials suchas dirt and moisture.

Other objects will be apparent from the description to follow and fromthe appended claims.

These objects are accomplished according to the preferred embodiment ofthe present invention by a foldable zoom lens system including a simpletriplet fixed portion and a zoom portion that includes areversed-telephoto front objective with a mirror between the negativeand positive components of the objective; a movable zooming component;and s compensating component. Another mirror is located between the zoomportion and the fixed portion to provide a compact zoom system that isfolded twice. A lens system according to the invention preferably isadapted to be focused for different subject distances by movement of therear component of the front objective, which enables the front lenscomponent of the system to be fixed so that the lens can be sealedagainst the entry of hannful materials.

BRIEF DESCRIPTION OF THE DRAWINGS In the detailed description of thepreferred embodiments, reference is made to the accompanying drawings,wherein:

FIG. 1 is a sectional view of a zoom lens system according to theinvention; and

FIG. 2 is a partial perspective view of portions of a cameraincorporating the lens system shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, a lenssystem according to the preferred embodiment of the invention is shown,the system including a zoom portion and a fixed portion. The zoomportion includes a reversed-telephoto objective I, a movable zoomingcomponent II for varying the magnification of the image, and anadjustable compensating component III that maintains the focus as thezooming component is adjusted. Behind the zoom portion is a beamsplitterB for directing a portion of the light from the zoom portion to a reflexviewfinder, shown in FIG. 2, and a fixed portion IV of the system forforming an image on the film plane of the camera in which the lens isincorporated. The front objective I includes a front negative meniscuscomponent l spaced relatively widely from a rear positive component 2.This reversed telephoto arrangement provides space for a mirror M tofold the optical axis of the lens Since reversed telephoto lenses arecharacterized by a relatively short focal length, which is equal to orshorter than the back focus, the objective I also provides a relativelywide field angle without significantly increasing the lens diameter.Component l is fixed in relation to the fixed portion IV, so that theentire lens can be sealed against dust, moisture and other harmfulmaterials. In addition, the fixed front component makes it possible todesign a camera having an uncluttered front portion. Component 2 isadapted for axial movement to focus the lens for various subjectdistances, which enables front component l to be fixedly mounted.Movement of component 2 to focus the lens does not alter the zoom rangeof the lens.

The magnification of the image formed by the front objective I is variedby axial movement of the zooming component II which consists of an airspaced doublet including a negative meniscus element 3 concave to therear and a weak negative meniscus element 4 concave to the front and inedge contact with the element 3.

' The compensating component III is a cemented doublet including a frontnegative meniscus element 5 and a rear biconvex element 6. Thecomponents II and III are mechanically coupled for opposed linear motionso that when component ll moves to change magnification, component IIImoves to maintain focus. Located between lens components II and III is adiaphragm D, and means (not shown) can be provided for adjusting thediaphragm aperture in response to displacement of the zoom components.Since the lens components II and III are located between the mirror Mand the beamsplitter B, they can be moved to vary magnification withoutinterference by reflectors. Thus, the system is provided with two foldsin the optical path without significantly lengthening the axial lengthElement N V Radiitmm.) Thicknesses or Separationstmm.)

R, 35.6 I L50 67 .0 3.48

S,=36.02 R, 32.6 2 L64 60 .l I,=2.73

S,=3.06 to |3.28 R, 51.8 3 L50 67 .0 1,-0.90

s,-2.|7 R, =-19.4 4 L50 67 .0 1 2.92

s,=|7.74 m 7.52 Diaphragm s,=7.z to 1.53

S.=2.02 to 7.67 R: z B 1.49 57.4 1,=1|.|3

5,-0.85 R,,= I31 7 L69 56 .2 I1=Z.58

s,=o.93 R,,=-l9.3 8 L62 36 .6 I =2.73

S,=0.83 R I23 9 l.6l 58 .8 t,=2.96

In the above table the lens elements are numbered from front to rearfrom 1 to 9 as shown in FIG. 1, N is the refractive index for each ofthe lens element materials for the D line of the spectrum, V is theindex of dispersion for each of the elements, and R, t and S are theradii of curvature, thicknesses, and spacings of the lens elements,numbered by subscript from front to rear.

The zoom lens described in the above table has a constant back focallength of 7.0 mm. and an overall length of 105.6 mm. and it is wellcorrected for apertures up to at least f./2.7. The equivalent focallength varies from 9.95 mm. to 22.42 mm.

In FIG. 2, an optical system according to the invention is shown mountedin a camera. Light from an object scene is transmitted by component 1 ofthe front objective to the mirror M which is positioned at an angle of45 with respect to the plane of component 1. The mirror reflects thelight towards component 2 which is mounted with its plane at 90 withrespect to the plane of component 1, so that the optical axes ofcomponents 1 and 2 are normal with respect to each other i.e., themirror puts a first fold in the system.

Component 2 is mounted by a ring 20 on a support plate 22 in the camera.Ring 20 is provided with a screw thread 23, and is axially movable inresponse to its rotation to focus the lens for different subjectdistances. The zoom component ll and the rear compensating component IIIare mounted in barrel mounts 24 and 26, respectively, which are slidablymounted on slide rods 28 for movement along the optical axis L of thesystem.

To contrplthe relative motion of theagomponents ll and ill, the cameraincludes a zoom mechanism, which may take many forms known in the priorart. The zoom mechanism shown in FIG. 2 includes a linking lever 30pivotally mounted on a pin 32 and having one end 34gpivotally connectedto a sleeve 36 attached to barrel mount 24,Fand the other end 38pivotally connected to a sleeve 37 attached to barrel mount 26 foreffecting opposed linear motion of the components II and 11!. Thus, therelative movement of these components is determined by the location offixed pivot pin 32 with respect to the ends of link 30. Movement istransmitted to the components by a bell crank 40 which is pivotallymounted on an axle 42. The bell crank 40 has a slot 44 at one end forreceiving a pin 46, and a control knob 48 at the other end accessiblefrom the exterior of the camera for actuation by an operator. The camerabody is provided with a recess 50 whereby knob 48 need not extend beyondthe surface thereof.

In response to vertical movement of knob 48, crank 40 pivots and urgessleeve 37 along slide rod 28 through the connection of pin 46 in slot44. Such horizontal displacement of sleeve 37 is transmitted by link 30to sleeve 36, which is urged in the opposite direction by the rotationof the link about its fixed pivot 32. The dimensions of link 30 are suchthat focus is substantially maintained throughout the zoom range. Asindicated above, an adjustable diaphragm D is located between thecomponents I! and Ill. It should be noted that all of the movable partsof the lens are located between the folds of the system, thussimplifying the structure of the means for moving the various lensmembers.

The beamsplitter B is located behind the compensating component ill, fortransmitting a portion of the light from the zoom portion along an axisL to a reflex viewfinder and for reflecting the remaining portion ofthat light through the fixed portion [V to the film plane of the camera.The beamsplitter B comprises a pair of prisms 52 and 54 having asemireflective interface 56 which transmits a portion of incident lightand reflects the remaining portion at an angle of It may thus be seenthat the beamsplitter B provides a second fold in the optical system.Light transmitted by' the beamsplitter passes through a viewfinder relay58 and is reflected by a prism 60 to an erecting prism 62 which in turndirects an upright image through a mask 64 and an eyepiece 66. Theprovision of a first fold at the front of the lens has made possible theincorporation of a compact prism arrangement for erecting the viewfinderimage, since only three additional folds are required in the viewfindersystem.

Thus, a compact zoom optical system has been provided which lends itselfwell to incorporation in a camera having a small depth, the system beingof relatively simple construction and additionally making possible theuse of a simple reflex viewfinder.

The invention has been disclosed in detail with particular reference toa preferred embodiment thereof, but it is to be understood thatvariations and modifications within the spirit and scope of theinvention will be apparent to those skilled in the art to which theinvention pertains.

We Claim:

1. A zoom lens comprising in spaced optical alignment: a front objectiveincluding a first negative component and a second positive componentspaced from the first component, a first zoom component comprising amovable doublet including two spaced negative elements, and a secondzoom component being a cemented doublet including a first negativeelement and a second positive element, said lens including a reflectorin the space between the components of the front objective, said lenselements having substantially the following characteristics and spatialrelations, wherein N is the index of refraction for the D line of thespectrum, V is the index of dispersion, the R, t and S referrespectively to the radii of curvature of the lens surfaces, the axialthicknesses of lens elements, and the axial spacings between the lenselements, num bered by subscript from front to rear:

Element N V Radii(mm.) Thicknesses or

1. A zoom lens comprising in spaced optical alignment: a front objectiveincluding a first negative component and a second positive componentspaced from the first component, a first zoom component comprising amovable doublet including two spaced negative elements, and a secondzoom component being a cemented doublet including a first negativeelement and a second positive element, said lens including a reflectorin the space between the components of the front objective, said lenselements having substantially the following characteristics and spatialrelations, wherein N is the index of refraction for the D line of thespectrum, V is the index of dispersion, the R, t and S referrespectively to the radii of curvature of the lens surfaces, the axialthicknesses of lens elements, and the axial spacings between the lenselements, numbered by subscript from front to rear: Element N VRadii(mm.) Thicknesses or Separations(mm.) R1 35.6 1 1.50 67 .0 t1 3.48R2 24.1 S1 36.02 R3 32.6 2 1.64 60 .1 t2 2.73 R4 -103.6 S2 3.06 to 13.28R5 51.8 3 1.50 67 .0 t3 0.90 R6 9.27 S3 2.17 R7 -19.4 4 1.50 67 .0 t42.92 R8 -54.8 S4 17.74 to 7.52 Diaphragm S5 7.2 to 1.53 R9 16.4 5 1.7229 .3 t5 0.97 R10 7.92 6 1.66 50 .8 t6 4.37 R11 -62.9 S6 2.02 to 7.67RB1 infinity B 1.49 57 .4 tB 11.13 RB2 infinity S7 0.85 R12 13.2 7 1.6956 .2 t7 2.58 R13 -267.8 S8 0.93 R14 -19.3 8 1.62 36 .6 t8 2.73 R15 9.56S9 0.83 R16 12.9 9 1.61 58 .8 t9 2.96 R17 -33.4